The invention relates to pressure-sensitive adhesive products for use in adhering to skin or like delicate surfaces.
Pressure-sensitive adhesive tapes and the like are used in a wide variety of applications where there is a need to adhere to skin, for example, medical tapes such as wound or surgical dressings, athletic tapes, surgical drapes, or tapes or tabs used in adhering medical devices such as sensors, electrodes, ostomy appliances or the like. A concern with all these adhesive coated products is the need to balance the objective of providing sufficiently high levels of adhesion to ensure that the pressure-sensitive tape products do not fall off, while ensuring that the underlying skin experiences the least amount of trauma, damage or irritation possible while the adhesive tape or the like is being used and/or removed. These goals are generally conflicting. Pressure-sensitive adhesives are known that are hypoallergenic in nature, minimizing allergic reactions. However, tape products using these adhesives can still damage or irritate skin. For example, lack of breathability can result in overhydration and sometimes maceration of the skin. Adhesives which tend to build in adhesion or have excessively high levels of initial adhesion can pull off skin cells or layers, particularly when the skin cells have lost some of their cohesion due to overhydration or maceration. These problems are particularly pronounced where tapes are repeatedly adhered to a given site. Each time a tape is removed, the underlying skin experiences a traumatic event removing further skin cells or layers, which damage can accumulate faster than the body can repair it. U.S. Pat. No. 5,614,310 addresses this problem by suggesting a particular adhesive layer formed using solvent-insoluble, solvent-dispersible, acrylate-based elastomeric pressure-sensitive adhesive microspheres optionally impregnated with an antimicrobial agent. The backing used with this adhesive preferably has a moisture vapor transmission rate (MVTR) value of at least 500 g/m.sup.2 /day (measured using ASTM E 96-80 at 40.degree. C.). This adhesive showed low levels of adhesion build-up to skin over time. Although acceptable for some uses, this adhesive is somewhat difficult to manufacture, still exhibits some adhesion build-up to skin over time, can cause moisture buildup, and lacks high levels of cohesion which can result in adhesive transfer to skin.
Another approach in the art to providing pressure-sensitive tapes and the like with low levels of skin irritation and/or damage has been the use of pattern coated adhesives. A discontinuous adhesive coating on a backing allows the skin to breathe, at least in the areas of the backing not coated with adhesive. This approach is disclosed in U.S. Pat. No. 4,595,001 (Potter); U.S. Pat. No. 5,613,942; EP 353972; and EP 91800. These patent documents generally teach intermittent coating of adhesives onto different backings. For example, U.S. Pat. No. 5,613,942 describes printing pressure-sensitive adhesives using a release coated calender roll process similar to Gravure printing. This patent also teaches screen printing. However, pattern coating or printing of adhesives in this manner is problematic as it generally requires solvents which are environmentally problematic and residual low molecular weight species can cause skin irritation. It would be preferred, from environmental, manufacturing (e.g. elimination of the need for expensive solvent recovery) and performance perspectives to have adhesives coatable directly from a melt phase.
EP Pat. Appln. No. 448213 addresses the problem of skin irritation by proposing coating the skin with retinoids either prior to applying the adhesive tape or by placing a retinoid layer on the adhesive layer itself However, this conditioning barrier layer can also interfere with adhesion. Similarly, U.S. Pat. No. 4,140,115 teaches use of a specific conditioning additive to an adhesive to reduce stripping of skin cells upon removal of a tape. The adhesive mass contains an unreacted polyol in an amount ranging from 4 to 20 weight percent. However, the polyol also reduces the adhesion force.
U.S. Pat. No. 4,024,312 suggests the use of an elastomeric backing which is stretched at a zero degree angle when removed resulting in the adhesive layer stretching and removing more easily. However, elastic tapes are difficult to handle and manufacture, adhesive tackifiers tend to migrate from the adhesive into the elastic backing, and it is difficult for the user to remember to remove the tape only in this one manner, which is different from how tapes are typically removed.
There remains a need for pressure-sensitive adhesive tapes that exhibit low trauma and irritation to skin in use and upon removal, particularly repeated use on the same site, regardless of the manner of removal and which are easily made from hot melt applied pressure-sensitive adhesives.